I own an iPad with 64GB of storage. Until the recent arrival of the 128GB iPad, mine was the largest-capacity model available — but it’s not enough. At the moment, I have less than 6GB of free space; when that dwindles away, I’m going to be in trouble.

That makes me exactly the sort of person Seagate has in mind as a prospective customer for its $199.99 Wireless Plus, the hard-disk kingpin’s second-generation drive aimed at owners of iPads and other mobile devices. (Its predecessor, which debuted in 2011, was originally known as the Seagate GoFlex Satellite.)

The Wireless Plus is a portable, battery-powered drive with a terabyte of storage (twice that of the Satellite) and built-in wi-fi, which lets it connect with gadgets which don’t have a USB port, such as the iPad, iPhone and most Android devices. In fact, it can connect to eight devices at a time and can stream HD video to three of them simultaneously. Seagate provided me with a unit for review.

At first blush, the Wireless Plus looks like a slightly chunkier fraternal twin of Seagate’s Backup Plus, the company’s standard-issue USB drive. The skosh of extra space inside makes room for a battery; Seagate says the drive can power itself for up to ten hours on a charge. It comes with a plug-in USB 3.0 adapter, which you can leave off if you only plan to use the drive in wireless mode — or you can swap in an optional adapter such as a $100 one for Thunderbolt, the fast connector used by Macs and a smattering of Windows PCs.

As with Seagate’s earlier wireless drive, this one packs its own wi-fi network. You connect to it from your device, and then the device can see the drive.

Wait, if you need to use your wi-fi connection to hook up with the Wireless Plus, does that mean you can’t get online at the same time? Nope — a new feature lets you tell the drive to connect to another available wi-fi network, then pass its internet connection through to your device, letting you browse the drive and the Internet on a single connection. Nice.

But when I tried to use my iPad’s built-in 4G LTE and the Wireless Plus simultaneously, I discovered that I couldn’t: Every website I tried to visit got redirected to Seagate’s browser-based interface. It may not be something Seagate can do anything about — if an iPad’s connected to a wireless network, it assumes it can get wi-fi from it and ignores the cellular connection — but it’s still a limitation.

On an Android device, Seagate’s app has access to the file system, and can move data back and forth between the drive and the gadget at will. But building an external hard drive that will work with an iPad or other iOS device is no cakewalk. Actually, the very notion runs counter to a basic philosophy of Apple’s mobile operating system, which is that you shouldn’t have to worry much about where your stuff is stored. Unlike a Windows PC or a Mac, iOS hides access to the file system; you can’t just decide to start storing items elsewhere.

Seagate gets around this fundamental issue primarily by providing its own app. (It’s available in versions for Android and Kindle Fire as well as iPad and iPhone.) Seagate Media allows you to move files between your gadget and the Wireless Plus, and includes built-in video and audio players, plus a file viewer. It’s a little world unto itself, largely replicated in a similar-but-not-quite-identical service you can pull up in your device’s browser.

Here are some of the things the Wireless Plus lets you do with an iOS device:

Stream or copy videos from the Wireless Plus to Seagate’s iOS app, which includes a built-in video player;

Stream videos from the drive to an Apple TV using Apple’s AirPlay technology;

Copy photos and videos from the iPad’s Camera Roll to the Wireless Plus;

Open documents stored on the Wireless Plus in iOS apps that support the “Open With” feature (which includes Apple apps such as Pages and plenty of third-party programs);

Save documents to the Wireless Plus from apps that support the WebDAV protocol, such as Apple’s Pages, Numbers and Keynote (although this doesn’t seem to be documented by Seagate);

Use the drive with DLNA player apps, such as 8player, some of which let you do things with your media that Seagate’s app does not.

The Wireless Plus also works fine with computers as a USB 3.0 drive. (If you use it with a Mac, as I did, you need to install an included driver that allows OS X to save files to the drive.) And that’s probably the way users of iOS devices will fill it with content such as movies and music, since Apple doesn’t make it easy to move most types of content off an iOS gadget and onto an external storage device.

Here are some things you can’t do:

Copy photos and videos from the Wireless Plus to the iPad’s Camera Roll or other albums so you can get at them from other apps (but: you can copy photos, one at a time, using Safari, and I was able to copy videos using iCab, a third-party browser);

Copy most of the documents and media you use within third-party iOS apps over to the Wireless Plus;

Listen to music stored on the drive using the iPad’s Music app or watch videos stored on the drive using the Videos app;

Back up your iPad, as you can do via iTunes or iCloud.

So is the Wireless Plus worth two hundred bucks? Yes, if you understand what it does. Within Seagate’s app, it can give you access to storage-hungry stuff, such as a humongous collection of videos, which would never fit on the device itself, and which would also be too piggy to store on a cloud service such as Dropbox. While it doesn’t let you expand your iOS device to an additional 1TB of freely-available space, it’s still a useful accessory — and a more highly-evolved take on the concept than its predecessor.

I have one of these and you can definitely copy all the photos to your camera roll. There is an icon for that once you select multiple pictures. You can either download to your Seagate Media app or directly to the camera roll. You can also play or download the music or videos directly to the seagate media app. This is an amazing app/hard drive combination and I would highly recommend it to anyone who really uses their device(s). If you inject cover art into an mp4 container, for example, they show properly on the file when viewing them in the seagate media app.